Neurological stimulators have been developed to treat pain, movement disorders, functional disorders, spasticity, cancer, cardiac disorders, and various other medical conditions. Implantable neurological stimulation systems generally have an implantable signal generator and one or more leads that deliver electrical pulses to neurological or muscle tissue. For example, several neurological stimulation systems for spinal cord stimulation (SCS) have cylindrical leads that include a lead body with a circular cross-sectional shape and one or more conductive rings (i.e., contacts) spaced apart from each other at the distal end of the lead body. The conductive rings operate as individual electrodes and may be implanted percutaneously through a needle inserted into the epidural space, with or without the assistance of a stylet.
Once implanted, the signal generator applies electrical pulses to the electrodes, which in turn modify the function of the patient's nervous system, such as by altering the patient's responsiveness to sensory stimuli and/or altering the patient's motor-circuit output. In SCS for the treatment of pain, the signal generator applies electrical pulses to the spinal cord via the electrodes. In conventional SCS, “low frequency” electrical pulses are used to generate sensations (known as paresthesia) that mask or otherwise alter the patient's sensation of pain. For example, in many cases, patients report paresthesia as a tingling sensation that is perceived as less uncomfortable than the underlying pain sensation.
As with any implantable device, battery life is an important design concern. If the supply voltage that is applied to the current-generating circuitry is too low, then the circuits will not operate as desired. On the other hand, if the supply voltage applied to the circuitry is too high, then battery power is being unnecessarily wasted and the battery will have to be re-charged sooner rather than later. The amount of supplied voltage that is above the level required to operate the circuitry is generally referred to as the current source supply voltage “headroom.”
As will be explained in detail below, the disclosed technology relates to circuitry for detecting if a supply voltage is insufficient to allow the current-generating circuitry in an implantable nerve stimulation device to operate properly.